In a typical cellular radio system or radio communications network, wireless terminals, also known as mobile stations and/or user equipments (UEs), communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipments (UE) such as mobile telephones, “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data via radio access network.
The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which identity is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the wireless terminals within range of the base stations.
In some versions, particularly earlier versions, of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a radio network controller (RNC). The RNC, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. Universal Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using WCDMA for wireless terminals. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to RNCs. In general, in LTE the functions of an RNC are performed by the radio base stations. As such, the RAN of an LTE system has an essentially “flat” architecture comprising radio base stations without reporting to the RNC.
The following description, for purposes of explanation, refers to LTE, WCDMA, UTRAN or evolved (E)-UTRAN. This does however not limit the applicability to other technologies.